NS1 of H7N9 Influenza A Virus Induces NO-Mediated Cellular Senescence in Neuro2a Cells

Abstract

Background/Aims: The novel avian H7N9 influenza A virus has been detected in brain tissues and associated with central nervous system (CNS) symptoms in infected human and mice. Roles of its virulence factor, NS1 protein in influenza virus infected neuron has yet to be explored. Methods: Nitric oxide (NO) release and inducible nitric oxide synthase (iNOS) expression in H7N9/NS1-expressed Neuro2a cells were detected by Griess test and western blotting. Cell proliferation rate of H7N9/NS1-expressing cells was recorded by Cell Counting Kit-8. Effects of H7N9/NS1 on cellular senescence were investigated by senescence-associated β-galactosidase (SA-β-gal) staining, immunofluorescent staining of phosphorylated heterochromatin protein 1γ (pHP1γ) and qPCR analysis of IL-6 and IL-8. Results: H7N9/NS1 in Neuro2a cells and primary cultured mouse cortical neurons increased the expression of iNOS and boosted NO release. Neuro2a cells constitutively expressing NS1 displayed a reduced proliferative ability, enhanced SA-β-gal staining, increased level of IL-6 and IL-8 and a typical punctuate structure of pHP1γ in nuclei. In addition, p38 MAPK was elevated in NS1-expressing Neuro2a cells. Reduced iNOS expression and subdued cellular senescence effect was found in p38 MAPK inhibitor-treated NS1-expressing Neuro2a cells. Conclusion: Our results suggest that H7N9/NS1 protein increases the iNOS expression and NO release in Neuro2a cells, which can induce cell growth arrest and cellular senescence.